CsPbI3 Films Research Articles

Ascorbic Acid‐Assisted Stabilization of α‐Phase CsPbI3 Perovskite for Efficient and Stable Photovoltaic Devices

The all‐inorganic α‐CsPbI3 perovskite with superb thermal stability and suitable band gap for light harvesting has been considered as a promising candidate for efficient perovskite solar cells (PSCs). However, the photoactive black α‐CsPbI3 is thermodynamically unstable and transforms spontaneously into nonphotoactive yellow δ‐phase at room temperature. Herein, a facile method is reported to prepare α‐CsPbI3 perovskite films with high stability at room temperature by mixing a small amount of ascorbic acid (AA) in the CsPbI3 precursor solutions. It is revealed that the interaction of AA with the CsPbI3 precursors could effectively inhibit the rapid crystallization of CsPbI3 and reduce the size of the coordination colloidal, and thus decrease the grain size of CsPbI3 for preparing long‐term stable α‐CsPbI3 films. The PSCs based on the AA‐stabilized CsPbI3 films exhibit reproducible photovoltaic performance with a champion efficiency of up to 11.44% and stable output of 11.30%, along with excellent stability, retaining more than 76% of its initial efficiency after aging in ambient conditions for 250 h without encapsulation. Most importantly, such low‐cost, solution‐processable inorganic PSCs with high performance also show promising potential for large‐scale preparation.

A Novel Route for Fabrication of Stable CsPbI3 Perovskite Thin Film by Thermal Evaporation

AbstractPerovskite thin films hold promise as a potential candidate for high efficiency solar cells. In recent years, a wealth of results has been published on CsPbI3 thin films. However, most of the literature reports that CsPbI3 perovskite films are prone to aging where black colored CsPbI3 films with cubic lattice change to yellow colored films with orthorhombic lattice upon exposure to ambient conditions. This poor stability presents itself as a major challenge in utilization of CsPbI3 for device applications. This manuscript presents an alternate route for fabricating stable CsPbI3 thin films using thermal evaporation. Experimentally, our samples were found to be stable, visually and structurally, over a period of six months. Even annealing of the samples did not induce structural changes.

Natrium Doping Pushes the Efficiency of Carbon-Based CsPbI3 Perovskite Solar Cells to 10.7%

SummaryThe CsPbI3 inorganic perovskite is a potential candidate for fabricating long-term operational photovoltaic devices owing to its intrinsic superb thermal stability. However, the carbon-based CsPbI3 perovskite solar cells (C-PSCs) without hole transport material (HTM) are currently disadvantaged by their relatively low power conversion efficiency resulting from the poor grain quality and mismatched energy band levels of the as-made CsPbI3 films. Herein we demonstrate that by doping Na into the CsPbI3 lattice, the grain quality is significantly improved with low defect density, and also, the energy band levels are better matched to the contact electrodes, affording a higher built-in potential. Consequently, the Voc of the C-PSCs is drastically increased from 0.77 to 0.92 V, and the efficiency from 8.6% to 10.7%, a record value for the CsPbI3 PSCs without HTM. Moreover, the non-encapsulated device showed virtually no performance degradation after 70 days of storage in air atmosphere.

Reduced-Dimensional α-CsPbX3 Perovskites for Efficient and Stable Photovoltaics

Summary Inorganic CsPbX3 perovskites have gained great attention owing to their excellent thermal stability and carrier transport properties. However, the power conversion efficiency (PCE) of solution-processed CsPbX3 perovskite solar cells is still far inferior to that of their hybrid analogues. Insufficient film thickness and undesirable phase transition are the two major obstacles limiting their device performance. Here, we show that by adopting a new precursor pair, cesium acetate (CsAc) and hydrogen lead trihalide (HPbX3), we were able to overcome the notorious solubility limitation for Cs precursors to fabricate high-quality CsPbX3 perovskite films with large film thickness (∼500 nm). We further introduced a judicious amount of phenylethylammonium iodide (PEAI) into the system to induce reduced-dimensional perovskite formation. Unprecedentedly, the resulting quasi-2D perovskites significantly suppressed undesirable phase transition and thus reduced the film's trap density. Following this approach, we reported a state-of-the-art PCE to date, 12.4%, for reduced-dimensional α-CsPbI3 perovskite photovoltaics with greatly improved performance longevity.

Efficient and High-Color-Purity Light-Emitting Diodes Based on In Situ Grown Films of CsPbX3 (X = Br, I) Nanoplates with Controlled Thicknesses

We report a facile solution-based approach to the in situ growth of perovskite films consisting of monolayers of CsPbBr3 nanoplates passivated by bulky phenylbutylammonium (PBA) cations, that is, two-dimensional layered PBA2(CsPbBr3)n-1PbBr4 perovskites. Optimizing film formation processes leads to layered perovskites with controlled n values in the range of 12-16. The layered perovskite emitters show quantum-confined band gap energies with a narrow distribution, suggesting the formation of thickness-controlled quantum-well (TCQW) structures. The TCQW CsPbBr3 films exhibit smooth surface features, narrow emission line widths, low trap densities, and high room-temperature photoluminance quantum yields, resulting in high-color-purity green light-emitting diodes (LEDs) with remarkably high external quantum efficiencies (EQEs) of up to 10.4%. The solution-based approach is extended to the preparation of TCQW CsPbI3 films for high-color-purity red perovskite LEDs with high EQEs of up to 7.3%.

Solution-processed field-effect transistors based on polyfluorene –cesium lead halide nanocrystals composite films with small hysteresis of output and transfer characteristics

We have designed and investigated electrical and optical properties of solution-processed organic field-effect transistors (OFETs) based on conjugated polymer PFO and perovskite –cesium lead halide nanocrystals (CsPbI3) composite films. It was shown that OFETs based on PFO:CsPbI3 films exhibit current-voltage (I-V) characteristics of OFETs with dominant hole transport and saturation current behavior at temperatures 200–300 K. It was found that PFO:CsPbI3 OFETs have a negligible hysteresis of output and transfer characteristics especially at temperatures below 250 K. The values of the hole mobility estimated from I-Vs of PFO:CsPbI3 OFETs were found to be ∼2.4 10−1 cm2/Vs and ∼1.9 10−1 cm2/Vs in saturation and low fields regimes respectively at 300 K; the hole mobility dropped down to ∼6 10−3 cm2/Vs and 2.8 10−3 cm2/Vs respectively at 200 K, and then down to 5.5 10−5 cm2/Vs at 100 K (in low field regime), which is characteristic of hopping conduction. The effect of sensitivity to light and light-emitting effect were found under application of negative source-drain and gate pulse voltages to PFO:CsPbI3 OFETs at 300 K. The mechanism of charge carrier transport in OFETs based on PFO:CsPbI3 hybrid films is discussed.